Submarine sonar systems include a towed sonar array that is deployed behind a moving submarine. The sonar sensor part of the towed array may be more than 1000 yards behind the submarine. This enables the total sonar system to detect other vessels and through triangulation establish an accurate distance to the detected vessel.
When the towed array is retrieved into the submarine it passes through an outboard sensor assembly (OSA), usually in the vertical stabilizer of the submarine. The outboard sensor assembly contains electronic instrumentation necessary to monitor the passage of the towed array during deployment, towing, and retrieval and to relay that information to submarine personnel.
Due to the corrosive environment of the ocean the housing of outboard sensor assemblies have been machined from Monel, an alloy containing nickel, copper, iron and other alloys, with nickel being the primary component, followed by copper and then iron. The resulting outboard sensor assembly is relatively difficult to machine, expensive, and heavy. The weight is important because divers often do repair of an outboard sensor assembly underwater while the submarine is in port. The Monel housing surrounds an interior passageway composed of either Monel or polymer through which the towed array passes. A common failure mode of this design is electrical shorting caused by seawater leaking into the interior of the Monel housing where electronic components are contained. These failures and the combination of the weight and costs of the system results in high operation and support costs of replacing failed units during submarine maintenance periods.
U.S. patent application Ser. No. 11/058,895, by the inventors described an OSA device for monitoring deployment of a towed array from a boat that includes a housing of a composite polymer; an interior passageway for movement of the towed array; and a pressure compensation bladder positioned between the housing and the interior passageway in which the pressure compensation bladder is mounted so that it's interior surface is in communication with the environment exterior to the apparatus, namely the ocean. Thus as the module descends or ascends through ocean depths the bladder expands or shrinks and maintains an interior oil pressure equal to the exterior pressure—eliminating any pressure differential that can lead to the electrical shorting caused by leakage of seawater into the interior of the housing where electronic components are contained.
The solution described in U.S. patent application Ser. No. 11/058,895 is very effective in solving the problem of seawater leakage into the interior of the housing. One issue however that can develop over time is a fouling or plugging of the pressure compensation bladder from seawater contaminants. Accordingly alternate systems that do not use such a pressure compensation bladder have been used. These devices, designed for the depths of the oceans, or in deep well environments, have passive pressure compensation systems that may consist of an interior filling of an incompressible material sealed in by some type of a mechanical seal such as for example an o-ring.
While this type of pressure compensation may work well in normal temperature ranges there are applications in which the devices may be exposed to extreme temperature swings and thermal expansion or shrinkage may be so large that the containment seals may fail.
What is needed therefore is a passive pressure compensation system that is balanced in such a way that the thermal expansion or shrinkage is manageable over an extreme temperature range. There is an unmet need then for a new outboard sensor assembly, one that is lower cost, easier to manufacture in quantity, lighter weight, and with a lower failure rate. The instant invention to be described meets those needs.